The correct answer is D.
The Cuban Missile Crisis of 1962 was a 13-day confrontation between the United States and the Soviet Union.
This confrontation was nearly the beginning of a full-scale nuclear war.
It was all about arms race and the deploying of ballistic missiles as a treat to the other country. The United States deployed the missiles in Italy and Turkey and the Soviet Union in Cuba.
After this crisis, the balance of power between the two countries was temporarily restored.